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FEATURE TERABIT NETWORKS


Tis paper uses network modelling to quantify the level of savings from a capacity-fixed approach. Tey show that a capacity-fixed approach offers reductions in line module and chassis counts leading to lower network cost.


Super-channels, slice by slice Some of you may be thinking ‘gosh, 1.2Tb/s is a lot of capacity to pay for in one chunk, and it’s also a lot of capacity to have running between the same two points’. Te first of these problems is solved by using the instant bandwidth economic model, in which super-channel capacity is activated (and charged for) in 100Gb/s increments using a soſtware license. Te second problem is solved by making the super-channel ‘sliceable’. Remember that all of these super-channels must


be optically routed as a single unit. In other words, a ROADM would have to manipulate the full 1.2Tb/s as a single chunk, and any sub-super-channel grooming would be achieved using OTN switching. Figure 3 shows how a super-channel can be


optically divided, by retuning the lasers on the super-channel line card. In a real implementation all of these lasers would be realised using large-scale photonic integrated circuits (PICs) to make it possible to implement so much capacity on a single


line card. In this example I have chosen to slice the original super-channel into three, separate 400Gb/s super-channels that are separated by guard bands. Te guard bands allow ROADMs to ‘get hold’ of


the individual super-channels so they can be directed over different paths. You will also notice that each super-channel is able to use a different modulation type. A production line card would typically be able to divide up the super-channel capacity with granularity of 100Gb/s in any combination, right down to the maximum of twelve 100Gb/s ‘channels’ separated by guard bands. Another use for this programmable modulation


16386 BBWF Advert 189mmx129mm_Layout 1 29/05/2015 16:55 Page 1


capability would be in protection scenarios, an example of which is shown in the lower part of Figure 3. Let’s imagine a 100Gb/s service is set up between A and B, a distance of less than 1,000km. Tis means that PM-16QAM modulation could be used. However, if there is a failure on the fibre between A and B, and only optical protection is used, the next shortest path would be A-C-B, which is between 1,000 and 2,000km long. Tis is too far for PM-16QAM, but we could reprogram the line cards to use PM-8QAM over the protection path. If there is another failure on the A-C link, we could reprogram the modulation to PM-QPSK and close the even longer link A-D-C-B.


Summary Coherent super-channels are the preferred technology for implementing high-capacity, long-haul DWDM services. Tey are also the only technology in production today that offers a clear path to scale continuously beyond 100Gb/s data rates and into the terabit scale for DWDM line cards. Te latest enhancements to this technology


provide a fully programmable modulation capability that open up new ways to reduce costs and enhance service quality while continuing to scale to the growing demands of today’s Internet.l


Geoff Bennett is the director of solutions and technology at Infinera


Explanation of terms: PM-BPSK: polarisation-multiplexed binary phase- shift keying; PM-QPSK: polarisation-multiplexed quadrature phase-shift keying; PM-3QAM, PM-8QAM, and PM-16QAM: polarisation-multiplexed 3, 8 and 16-state quadrature amplitude modulation.


Further reading l Geoff Bennett. ‘Super-Channels: DWDM Transmission at 100Gb/s and Beyond’. Infinera White Paper. l Onur Turkcu, Soumya Roy, Abishek Gopalan, Matt Mitchell, Biao Lu. ‘Comparing Networks with Capacity- fixed and Spectrally-fixed Line Modules Implementing Multiple Coherent Modulations’. ECOC 2015.


We're Moving to London 15th Annual


2015 #BBWF2015@BBWorldForum


Bringing Fixed Mobile Convergence to Life! Optimize & Monetize Fixed,Mobile and CloudNetworks


20-22 October 2015 |ExCeL, London, UK www.broadbandworldforum.com


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